1. Field of the Invention
The present invention is directed to a method for operating an medical imaging diagnostic apparatus.
2. Description of the Prior Art
Medical imaging diagnostic apparatuses include ultrasound devices, X-ray computed tomography devices and magnetic resonance devices. Magnetic resonance technology is a known technique for acquiring images of the inside of the body of an examination subject. In a magnetic resonance apparatus, rapidly switched gradient fields that are generated by a gradient system are superimposed on a static basic magnetic field that is generated by a basic magnet system. The magnetic resonance apparatus also has a radio-frequency system that beams radio-frequency signals into the examination subject for triggering magnetic resonance signals and that picks up the resulting magnetic resonance signals, on the basis of which magnetic resonance images are produced.
In functional magnetic resonance imaging, for example, datasets are registered in a time sequence from the same region of an examination subject to be imaged. Corresponding methods are known for recognizing and correcting differences between the datasets that are the result of a positional change of the imaged region with respect to the apparatus during the time sequence.
One group of methods for determining positional changes from chronologically successively registered datasets is based on a description of an arbitrary rigid body movement in the three-dimensional space by means of six motion parameters, three parameters characterizing translations and three parameters characterizing rotations. The general motion of the rigid body is linearized, for example, by means of a Taylor development of the first order involving all or selected picture elements of two datasets to be compared, the parameters then being able to be determined therefrom, for example using of an iterative method.
In another group of methods for dataset-based acquisition of positional changes, all or specifically selected points of a first dataset described in k-space and of a second dataset that has been generated temporally following the first are compared to one another. These methods are based on the fact that, due to a positional change between the exposure times of the two datasets, translations and/or rotations of the imaged region are reflected in a variation of phase and/or amounts of the data points given a comparison of data points arranged within the two datasets. The navigator echo technique also is an example of a method of this further group.
Further details about functional magnetic resonance imaging and the methods for acquiring and correcting positional changes employed therein are described, for example, in the article by S. Thesen et al., “Funktionelle Magnetresonanztomografie in Echtzeit”, electromedica 68 (2000) No. 1, pages 45-52.
Further, methods are known wherein—differing from methods based on rigid bodies—deformations of the region of interest are permitted over the course of the time sequence for determining positional changes from chronologically successively registered datasets. Further details with respect thereto are described, for example, in the book by J. Hajnal et al., Medical Image Registration, CRC Press, 2001, chapter 13, “Dave Rueckert: Nonrigid registration. Concepts, Algorithms and Applications”.
For monitoring the progress of a therapeutic regimen, it is standard to repeatedly image a region to be monitored in an examination subject by means of successive and temporally spaced image or data acquisitions (examinations) with a medical diagnosis apparatus. The examinations thereby ensue, for example, with a temporal spacing of a few hours or weeks. In an examination temporally following a first examination, an operator of the diagnosis apparatus thereby attempts to position the examination subject in the diagnosis apparatus by means of manual inputs so that the images to be registered optimally correspond to those of the first examination as to positioning within the examination subject. Only a moderate degree of coincidence is achieved by such the manual adjustment. Further, the degree of coincidence is dependent on the operator. Moreover, such manual adjustment is comparatively time-consuming.